Coal is a fossil fuel formed primarily from vegetable matter decomposed without access to air under the influence of pressure, temperature, and moisture. Specifically, the process of coal formation begins with the accumulation of vegetable matter. The weight of the top layers of vegetable matter compact the lower layers. This is done primarily by squeezing out large amounts of water. Over time, the plant material is buried further by sediments with the loss of water and volatile materials resulting in the formation of lignite. With increasingly deeper burial increases in pressure occur that compress the lignite. The resulting compression effected by the increasing depth of burial further devolatilizes the coal so that the rank of coal becomes progressively higher rising from lignite to sub-bituminous, bituminous, semi-anthracite, anthracite and meta-anthracite stages.
As a result of the formation process, coal is generally found horizontally inclined underground in sedimentary rock sequences. Geologic/tectonic activity, however, causes these sequences or strata to be gently folded pitching the coal seams at inclines of up to 40-45%. While modern mining equipment operates with a relatively high degree of efficiency on moderate grades, operating problems limit or effectively prohibit operation of such equipment in seams pitched greater than approximately 10%.
More specifically, continuous miners are unable to maintain the necessary grip or traction to efficiently cut coal when either transversing or following step grades. Likewise, conventional mining equipment is difficult to bring into proper position for mining step grades. Further, step grade mining subjects the mining equipment to unusual stress that the equipment was not designed to bear. Accordingly, significant maintenance problems result leading to an increase in downtime for costly repairs and lost productivity. Thus, it should be appreciated that if pitched seam coal reserves are to be recovered, the need exists for the development of efficient and effective mining equipment for this purpose.